<!DOCTYPE html>
<html>
    <head>
        <script src="vue.js"></script>
    </head>
    <body>
        <div id="app">
            <p>总价格: {{totalPrice}}</p>
            <p>单价: {{price}}</p>
            <p>数量: {{num}}</p>
            <div>
                <button @click="num == 0 ? 0 : num--">减少数量</button>
                <button @click="num++">增加数量</button>
            </div>
        </div>
        <script>
            var vm = new Vue({
                el:'#app',
                data:{
                    price:20,
                    num:0
                },
                computed: {
                    //总价格totalPrice 
                    totalPrice () {
                        return this.price * this.num
                    }
                }
            })
        </script>
    </body>
</html>